Apparatus and method for automated contact tasks

ABSTRACT

An apparatus for automated contact tasks and a related method are described. The apparatus includes a mechanical interface for connecting the apparatus to a manipulator, a holder for receiving a tool and being movable in relation to the mechanical interface, at least one actuator for positioning the holder in relation to the mechanical interface, a sensor unit that senses the actuator force provided by the at least one actuator, and a control unit that sets the actuator force to a desired minimum force to press the holder against a stop, while there is no contact between the tool and a surface, and detects contact when the holder moves in relation to the mechanical interface in opposition to the direction of the desired minimum force. The control unit further regulates the actuator force according to a pre-programmed contact force time-characteristic, when contact between the tool and the surface has been detected.

TECHNICAL FIELD

The present disclosure relates to an active handling apparatus as wellas to a method for automated contact tasks (manipulating and positioningtasks) such as, for example, the robot-supported processing (machining)of surfaces or the manipulation of machine elements or workpieces duringoperations such as, for example, mounting, stacking, sorting, etc.

BACKGROUND

Different apparatuses are known for robot-supported, automated contacttasks such as, for example, the processing (machining) of surfaces(e.g., grinding, polishing, etc.) as well as the manipulation ofworkpieces or machine elements (stacking, palletizing, mounting, etc.).The grinding apparatus described in publication U.S. Pat. No. 5,299,389can be named as an example. In the case of this apparatus, a rotatinggrinding disk is moved toward the surface to be ground by means of anindustrial robot. The contact between the grinding disk and the surfaceis recognized by means of the load current of the motor driving thegrinding disk, which provides a method which is too imprecise for manyapplications. In general, in the case of robot-supported automatedsystems where the robot contacts an object, the problem consists inrecognizing the moment of contact and the closed-loop control of thecontact force.

Even in the case of modern, force-regulated systems, when the tool whichis mounted on the robot contacts the surface to be contacted ashock-like contact force occurs which may not be a problem in manycases, but in applications where precision is crucial or where verysensitive workpieces have to be processed or machined, it is extremelytroublesome and undesirable. It is only possible to regulate the contactforce once the robot has contacted the surface, and consequently inpractical applications the mentioned shock-like contact force is anecessary evil which can certainly be reduced (for example by insertinga passively flexible element in the drive train) but cannot beeliminated. The passive flexibility of a spring, however, acts in anuncontrolled manner and can disturb the desired process.

Known force-regulated systems are frequently not able to react quicklyenough in the case of very rapid (i.e. high-frequency) disturbances,such as, for example, jerks or impacts, as the regulated drive train hasa certain inertia which results in a corresponding reaction time. In thecase of rigid systems (such as, for example, standard industrial robots)even the smallest displacements, if effected too quickly, will result ina high increase in the force.

In view of the above, there is a general need for an active handlingapparatus (effector) for a manipulator such as an industrial robot,wherein the handling apparatus should be designed for the purpose ofcontacting surfaces in a practically jolt-free manner and subsequentlyof jerk-free control of the contact force.

SUMMARY

A handling apparatus for automated contact tasks is described herein. Inaccordance with one exemplary embodiment, the handling apparatusincludes the following components: a mechanical interface for releasablyor fixedly connecting the handling apparatus to a manipulator; a holder,which is movable in relation to the interface, for receiving a tool; atleast one gearless actuator for positioning the holder in relation tothe interface to the manipulator; a sensor unit for directly orindirectly determining the force acting on the at least one actuator;and a closed-loop control unit which is configured to control the atleast one actuator to press the holder at an adjustable minimum force(F₀) against a stop as long as there is no contact between the handlingapparatus and a surface, and to control the contact force (over time)when there is contact between the handing apparatus and the surface,wherein once contact has been recognized, the contact force is increasedfrom the minimum force (F₀) to a predeterminable desired force(F_(DESIRED)).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdescription and drawings. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures, likereference numerals designate corresponding parts. In the drawings:

FIG. 1 shows a representation of a robot-supported automated grindingdevice with a manipulator, a grinding machine and a handling apparatusfor the grinding machine which is arranged between the manipulator andthe grinding machine;

FIG. 2 illustrates by means of a schematic diagram an example of ahandling apparatus as claimed in the invention with one degree offreedom, a bellow-type pneumatic cylinder working in opposition to aspring provided as an actuator;

FIG. 3 shows a detailed sectional representation of a handling apparatuswhich is constructed according to the example from FIG. 2;

FIG. 4 illustrates by means of a schematic diagram a further example ofa handling apparatus with one degree of freedom, a pneumatic muscleworking in opposition to a spring provided as an actuator;

FIG. 5 illustrates by means of a schematic diagram a further example ofa handling apparatus with three degrees of freedom, three bellow-typepneumatic cylinders working in opposition to a spring provided as theactuators;

FIG. 6 illustrates the regulated force (over time) when effectingcontact between the tool and the workpiece as well as loss of contact;

FIG. 7 illustrates the force-displacement characteristic curves ofsprings and cushion-type pneumatic cylinders as well as an adaptedspring characteristic curve;

FIG. 8 shows a lever mechanism for adapting the force-displacementcharacteristic curve of a spring; and

FIG. 9 illustrates (a) the relationship between the spring length andthe distance between plates established by the mechanism from FIG. 8 aswell as (b) the adapted force-displacement characteristic curve of themechanism from FIG. 8.

DETAILED DESCRIPTION

A prerequisite for the absence of static-friction and jerking of theactuator is the use of gearless actuators. These types of actuators are,for example, pistonless, pneumatic actuators (bellow-type pneumaticcylinders and pneumatic muscles), pneumatic cylinders with a pistonmounted in a static friction-free manner (for example a glass cylinderwith a graphite piston or other material combinations) and gearless,electric linear units with an armature mounted in a static-friction-freemanner (for example air-bearing or magnetic-bearing armatures). In thepassive (i.e. non-regulated) case, very flat force-displacementcharacteristic curves of the handling apparatus can be achieved usingthese types of actuators.

FIG. 1 illustrates, as one exemplary embodiment, a representation of arobot-supported automated grinding device with an industrial robot as amanipulator 20, a grinding machine 40 as a workpiece and a handlingapparatus 30′, which is arranged between an end effector flange 21 ofthe manipulator 20 and the tool 40 and is used substantially forprecision control or for closed-loop controlling in a precise manner themovement of the tool 40 in relation to a workpiece 50 to be machined aswell as for closed-loop controlling of the force exerted onto theworkpiece 50 by the tool 40. The construction of the manipulator 20 isof secondary importance. A standard industrial robot with four armsegments 20 a, 20 b, 20 c and 20 d is used in the present example. Thetask of the manipulator essentially consists in positioning the tool 40in an operating position on or above the workpiece 50 to be machined.Closed-loop controlling of the position in a precise manner and inparticular closed-loop controlling of the force in a precise manner iscarried out by means of the handling apparatus 30′. This latter isrealized in the present case for the purpose of moving the tool 40(grinding machine) toward the workpiece 50 and, on contact, for exertinga contact force onto the workpiece 50. Thus, for example, a grindingdisk of the grinding machine is able to be pressed onto the workpiece 50at a certain force in order, for example, to obtain a certain grindingeffect. As a result of closed-loop controlling of the force, the forcecan then also be held, for example, constant if the grinding disk ispartly worn. To control the force, it is necessary to determine ameasuring variable for the contact force which can be realized, forexample, by means of a load cell or by means of the motor current of thegrinding machine. An example of an automatic grinding device shown inFIG. 1 is explained in more detail, for example, in publication U.S.Pat. No. 5,299,389.

Precise positioning of the tool 40, as well as controlling the forcewith only the manipulator would be possible, in principle, but doing soplaces very high demands on the manipulator. Precise positioning, aswell as controlling the force in an exact and rapid manner as may bedesired, for example, for many contact tasks, is only possible usingvery expensive manipulators. For this reason, a handling apparatus whichcarries out the abovementioned positioning and force regulating task issituated between the end effector flange of the manipulator and theactual tool (e.g. grinding or polishing machine, gripper, etc.). Theaccuracy demands that the manipulator must fulfill can then berelatively small. Such types of handling apparatuses are also called“active flanges”.

In general, in the case of robot-supported or automated systems wherethe robot contacts an object, the problem is recognizing the moment atwhich contact is made and regulating the contact force. It is notpossible to regulate the contact force until the robot has contacted thesurface. For this reason, in the case of all known force-regulatedsystems, a shock-like contact force initially occurs when contact ismade between the tool mounted on the robot and the surface to becontacted. t Not only the mass (i.e. the inertia and consequently thekinetic energy) of the tool and of the handling apparatus is present inthis impact force, but also the mass or the kinetic energy of the entiremanipulator together with the drives. This mass essentially determinesthe impact energy (to be avoided).

The resultant shock-like contact force may not be a problem in manycases, however in applications where precision is important or verysensitive workpieces have to be machined or treated, it is extremelydisturbing and undesirable. This means that the actual force overshootsin comparison to the desired force. Also during the machining of asurface (or during the handling of an object) the position of the toolhas to be adjusted in order to maintain the desired contact force. Inthis case, above all it is the effects of static-friction (the co-called“stick-slip effect”) which can lead to transient overshooting in thecontact force. In addition, in the case of geared drives the meshing ofthe teeth of the gear wheels can cause unwanted jerky impacts ofvibrations. When handling or machining objects, both effects can lead toquality defects.

The above-explained overshooting is usually reduced in robotics byinserting passive elastic elements into the drive train. Said elements,however, act in an uncontrolled manner and are consequently not usablefor precise handling and contact tasks, as their mechanically definedperformance characteristic (force-displacement characteristic curve) isfixedly predetermined and is not controllable in an automated manner.

FIG. 2 shows an exemplary embodiment of a handling apparatus (activeflange). A first flange part of the apparatus forms an interface 31 to amanipulator (for example to the end effector flange 21 of themanipulator 20 from FIG. 1). A second flange part 32 forms a holder 32for a tool (such as, for example, a grinding machine or a grippingmeans). A static friction-free linear actuator which, in the presentexample is realized as a bellow-type pneumatic cylinder 34, is arrangedbetween the two flange parts. Static friction-free actuators are, forexample, bellow-type pneumatic cylinders and pneumatic artificialmuscles (PAMs). As an alternative to this, it is also possible to usepneumatic cylinders with a piston mounted in a static friction-freemanner which usually consist of glass and operate with a graphitepiston. A further alternative is provided by electric direct drives, inparticular gearless linear drives which are mounted in a staticfriction-free manner (e.g. by means of ball-bearings, magnetic orair-cushion bearings). These types of drives are also inherentlyelastic, either as a result of the compressibility of the air (in thecase of pneumatic actuators) or as a result of the magnetic restoringforce (in the case of electric direct drives).

The apparatus additionally includes a guide device 35 which blocks allthe degrees of freedom of movement, with the exception of the degree offreedom of movement of the static friction-free linear actuator 34. Theguide device 35 must also not allow any notable static-friction betweenit and the shaft 352 guided therein. Said freedom from static-frictioncan be ensured, for example, by the use of roller bearings such as, forexample, linear ball bearings, in particular recirculating ballbearings. In the example shown in FIG. 2, a rotationally fixed shaftguide 35, 352 is provided with recirculating ball bearings 351.Consequently, the handling apparatus has precisely one degree offreedom, namely a translatory movement in the direction of thelongitudinal axis 353 of the shaft guide 35 which lies naturallyparallel to the longitudinal axis 343 of the linear actuator(bellow-type pneumatic cylinder 34).

A compressor 60 generates the necessary overpressure in the pneumaticsystem in order to drive the pneumatic linear actuator 34. In this case,the bellow-type pneumatic cylinder 34 shown in FIG. 2 can only generatea compression force on extension. The abovementioned pneumaticartificial muscle, in contrast, only generates a tensile force oncontraction. For this reason, a restoring force, which is provided, forexample, by a (tensile or compression) spring, has to act on the linearactuator. In the example from FIG. 2, the shaft 352 of the shaft guideis held back by the compression spring 36 such that a pre-stressed forceacts on the top flange part (holder 32) in the direction of the bottomflange part (interface 31 to the manipulator). The linear actuator 34 ismoved actively in opposition to said pre-stressed force. The pressure inthe linear actuator 34 is generated by means of the compressor 60 and isadjustable by means of an electronically actuated control valve 61 inaccordance with a desired value (desired pressure). The actual pressurein the linear actuator 34 (actual pressure) is measured using a pressuresensor 62. In addition, a linear potentiometer is provided as adisplacement sensor 63 which supplies a measured value for the currentdisplacement of the linear actuator 34 and consequently the relativeposition of the holder 32 (in relation to the interface 31 to themanipulator or in relation to the end effector flange of themanipulator).

The pressure-dependent force-displacement characteristic curve of thepneumatic linear actuator is usually known so that the actuator forceprovided by the linear actuator 34 on the flange parts 31 and 32 isaccessible to indirect measurement. I.e. the actuator force can easilybe calculated from the measured pressure in the actuator and themeasured deflection (lift) of the actuator. In this case, theforce-displacement characteristic curve of pneumatic linear actuators isusually provided with a hysteresis so that the direction of the movementis also included in the force calculation. In the case of an electricdirect drive, the actuator force could, for example, be determined in asimilar manner by means of a characteristic curve e.g. by means ofcurrent consumption.

The restoring spring force can also be calculated from theforce-displacement characteristic curve of the spring and of themeasured deflection. If a tool which is fastened on the holder 32 of thehandling apparatus contacts a workpiece, the difference between theactuator force and the restoring force is then the net force exertedonto the tool, which can be regulated in a conventional manner. In orderto determine from this the force that actually acts on the surface, theweight of the tool 40 (cf. FIG. 1) and its spatial position in relationto the surface of the workpiece must additionally be taken intoconsideration.

It is possible to regulate the position with only the measured value forthe deflection of the actuator 34 without any contact. In addition, theflexibility (or rigidity) of the handling apparatus 30 can be regulated(impedance regulating), i.e. the rigidity of the arrangement producedfrom the linear actuator and the restoring spring is regulated inaccordance with a desired value.

As a result of the elasticity inherent to a pneumatic actuator and thefreedom from static-friction of the arrangement, the aforementionedovershooting of the contact force is reduced to a minimum. As a resultof said elastic performance characteristic, the mass and inertia of themoved elements of the manipulator (robot arms and drives) is uncoupledfrom the tool and, as a result, from the workpiece in the effectivedirection of the elasticity. Consequently, only the much smaller mass ofthe tool is decisive to the kinetic energy. This reduces the impactenergy mentioned above when contact between the workpiece and the tooltakes place.

In addition, as a result of the freedom from static-friction and of thegearless drive, overshooting of the contact force is almost completelyeliminated in operation when there is active force regulation.Regulating the force in a jerk-free manner is therefore made possiblewhereas, in the case of conventional handling apparatuses, unwantedvariations always occur in the contact force as a result of the effectsof static-friction, it not being easily possible to compensate for theseunwanted variations by means of regulation.

FIG. 3 shows a detailed sectional representation through the handlingapparatus which is constructed according to the principle shown in FIG.2. The active flange shown includes a first flange part 31 as theinterface to the manipulator, the end effector flange 21 of which isshown, for example, in FIG. 1, as well as a second flange part 32 as theholder or receiving means for a tool. The geometry of the two flangeparts is standard in robotics. A housing part 37, in which both thecontrol valve 61 and the static friction-free shaft guide are arrangedwith a restoring spring in accordance with the same principle as shownin FIG. 2, is rigidly connected to the first flange part 31. Forprotection against dust and other contaminants, a shock absorber isprovided as a cover 39 between the flange parts 31 and 32. Said covercan also be realized in a liquid and/or dust tight manner for use underwater, in a rough environment or in clean rooms. The bellow-typepneumatic cylinder 34 serves as the static friction-free, gearlesslinear actuator. The linear actuator is arranged between the firsthousing part 37 and a second housing part 38 which is rigidly connectedto the holder 32.

The displacement sensor 63 shown in FIG. 2 is covered in the presentexample by the guide device 35 and cannot be seen. The pressure sensorand the compressor are not included in the representation from FIG. 3for reasons of clarity. Connections for the inlet air duct and outletair duct 38 can be arranged, for example, in the first housing part 37.The connection to the inlet air duct is, for example, connected to thecompressor 60 via a hose. The connection for the outlet air duct is, forexample, covered by a sound absorber. For underwater applications, theoutlet air duct can also be connected to a hose which directs the outletair up to the surface of the water in order to prevent the inflow ofwater into the pneumatic system. As a result of the outlet air ductbeing implemented as a hose, outlet air is also prevented from flowingout in the case of sensitive processes.

FIG. 4 shows a further exemplary embodiment of a handling apparatus,where a pneumatic artificial muscle 34′ is used in place of abellow-type pneumatic cylinder. The spring 36 in this example isarranged such that the two flange parts 31, 32 (the holder and theinterface to the manipulator) are pressed apart from one another, whilethe pneumatic artificial muscle 34′ exerts a tensile force which isdirected in opposition to the spring force. For the rest, thearrangement from FIG. 4 is designed in an identical manner to theexample shown in FIG. 2. In the pressure-free state, the apparatus fromFIG. 4, however, moves into an end position at maximum deflection,whereas the apparatus from FIG. 2 moves into an end position at minimumdeflection (i.e. distance between the flange parts 31 and 32), which canbe advantageous for safety reasons.

Quite generally speaking, the advantage of the apparatus according tothe embodiments described herein is, among others, that in the case ofloss of energy, the system is pulled back into a start position andnevertheless remains passively movable. Even after an emergency shutdown(e.g. on account of exceeding an admissible maximum force) the apparatusremains passively supple and any possibly jammed parts are able to bereleased.

FIG. 5 shows a simplified representation of a further exemplaryembodiment. The handling apparatus (active flange) shown in FIG. 5 hasthree degrees of freedom compared to the examples shown in FIGS. 2 to 4,namely one translatory degree of freedom (displacement in the directionof the longitudinal axes of the bellow-type pneumatic cylinders 34 a, 34b, 34 c) and two rotational degrees of freedom (tilting about tworotational axes which lie normally with respect to the longitudinal axesof the bellow-type pneumatic cylinders 34 a, 34 b, 34 c). In the case ofthree degrees of freedom, it is also necessary to have three staticfriction-free pneumatic linear actuators 34 a, 34 b, 34 c which arearranged in the present case evenly around a center axis of the handlingapparatus. The remaining design of the handling apparatus such as, forexample, the actuation of the static friction-free pneumatic linearactuators is, in principle, identical to the examples from FIGS. 2 to 4.The static friction-free guide device 35 is also constructed in asubstantially identical manner to the example from FIG. 4 (in thepresent case, a tension spring 36′ is used to generate a restoring forcefor the bellow-type pneumatic cylinder), however, the guide shaft 352 isnot rigidly connected to the top flange part (which forms the holder32), but is connected, for example, by means of a ball joint or a Cardanjoint (not shown) in order to make the abovementioned tilting movementpossible. Depending on the application, the joint can be rotationallyfixed so that (as in the present example) only tilting movements of thetop flange part are possible but not rotation.

The restoring force does not in principle have to be generated by aspring, but could also be provided by a second static friction-freepneumatic linear actuator. Thus, for example, in the example from FIG. 2a pneumatic artificial muscle (PAM, cf. FIG. 4) which is arrangedparallel to the bellow-type pneumatic cylinder could also be usedinstead of the spring 36. As an alternative to this, the use of adouble-acting static friction-free pneumatic cylinder is also possible.

In FIG. 6, the force regulation (force control) implemented in thehandling apparatuses according to the embodiments described herein isexplained again in more detail. FIG. 6a shows the (regulated) timecharacteristic of the contact force (force over time) in one exemplaryembodiment, FIG. 6b shows a schematic representation of the control unit80 (closed-loop control unit) of the actuator, which drives the handlingapparatus, in the present case a double-acting pneumatic cylinder 81with a piston, which slides within the cylinder in a practically staticfriction-free manner. FIG. 6c illustrates the advantage of the very flatforce-displacement characteristic curve of the handling apparatus in thepassive (non-regulated) case, ensuring that the impact forces on contactwith the workpiece are very slight.

In FIG. 6a the time-characteristic of the force F(t) exerted on theworkpiece by the handling apparatus 30 is shown, the force F beingregulated to a minimum value F₀ when there is no contact between thehandling apparatus 30 and the workpiece 50 (cf. FIG. 1). The minimumforce F₀ can be approximately zero, just large enough for the handlingapparatus 30 to remain still fully extended (or, depending on thedirection of force, fully retracted). In this state, contact monitoring,which activates the regulating of the contact force when a contact iseffected, is active. In the example shown in FIG. 6a , at moments t<t₀and t>t₃ there is no contact between the handling apparatus 30 and theworkpiece 50 (more precisely, the contact occurs indirectly by means ofthe tool 40 which is mounted on the handling apparatus) and thepneumatic control means 80 holds the holder 32 of the handling apparatus(cf. FIG. 2) at minimum force F0 against an end stop. In the presentexample, contact is recognized at moment t₀. In order to ensure as“supple” a contact as possible, a very small starting force F₀ (ideallyzero) is necessary. Once contact has been recognized, the holder 32 ofthe handling apparatus 30 is no longer held against the end stop and thecontact force is increased linearly to a desired force F_(DESIRED) whichis desired or necessary for the respective contact task (e.g. polishing,grinding, etc.). The increase in force from the minimum force F₀ to adesired force F_(DESIRED) is effected inside a defined time intervalT_(R). In the present example, the desired force is obtained at momentt1 and the workpiece 50 is processed (or handled in another manner) bymeans of the handling apparatus. During this, contact monitoring by thecontrol means 89 is again active in order to recognize a possible lossof contact.

In the present example, such loss of contact occurs at moment t2. Asreaction to this, the holder 32 of the handling apparatus 30 is movedagainst the end stop again and the control means reduces the forceinside a time interval T_(R) from the desired force F_(DESIRED) to theabovementioned minimum force F₀ in order to develop new contact, againin as “supple” a manner as possible. In the present case, the ramp-likeincrease after contact and the ramp-like drop in force after loss ofcontact are the same length (in both cases T_(R)). Depending on theapplication, the drop in force on loss of contact can also be effectedmore rapidly (e.g. force withdrawn as quickly as possible by means ofpressure-less switching of the pneumatic cylinder).

FIG. 6c illustrates the mentioned gentle contact between the handlingapparatus and the workpiece by way of a force-displacementcharacteristic curve. The passive (i.e. non-regulated)force-displacement characteristic curve of the handling apparatus can beset in a very flat manner (continuous characteristic curve) by means ofa suitable mechanical structure of the handling apparatus as mentionedabove. It will be possible to obtain values of, for example, only threeNewton per millimeter displacement. In comparison with this, knownforce-regulated systems are relatively rigid and are not able to reactquickly enough in the case of very rapid (i.e. high-frequency)disturbances, such as, for example, jerks or impacts, as the regulateddrive train has a certain inertia which results in a correspondingreaction time. In the case of rigid systems (such as, for example,standard industrial robots) the smallest displacements Ls, when they areeffected too rapidly, will result in a high increase Δf_(rob) in theforce, whereas the handling apparatus, as a result of its flatcharacteristic curve, brings about a negligibly small change in forceΔF_(Flange) and the regulating of the force is gently applied only aftercontact has been recognized.

Details of different possibilities for contact recognition and forrecognizing loss of contact are given again below. The abovementionedminimum force F₀ and the desired force F_(DESIRED) always have the samepreceding sign and the holder 32 always moves against the respective endstop when there is lack of contact. The end position can be recognized,for example, by means of the displacement sensor 63 (see FIG. 2). Whenthe holder 32 of the handling apparatus 30 is situated in an end stop,it can be generally assumed from this that there is no contact betweenthe handling apparatus 30 and the workpiece 40.

Proceeding from this state (holder 32 against an end stop), contact isdetected as soon as the holder 32 moves in opposition to the desiredforce F_(DESIRED) (for example a change in position detected by thedisplacement sensor 63) in relation to the manipulator interface 31. Asat this moment the force is regulated to a minimum value F₀ and as apneumatic actuator basically has a natural flexibility, the contact isvery gentle and there are no jerks between the handling apparatus 30 andthe workpiece 50.

Loss of contact is recognized, for example, whenever the change in thespeed of the holder 32 of the handling apparatus 30 exceeds apredeterminable acceleration value. The speed of the holder 32 withreference to the manipulator interface 31 at the moment of the loss ofcontact is stored. If the speed again drops (without an end stop beingreached), contact is again recognized. The change in speed can bemeasured either by means of the displacement sensor 62 or by using anacceleration sensor.

One problem that occurs in a good many practical applications resultsfrom the non-identical force-displacement characteristic curves of thebellow-type pneumatic cylinder or the pneumatic artificial muscle inrelation to the spring (cf. characteristic curve diagram in FIG. 7).While springs generally have a restoring force which increases linearly(from the relaxed state) as the deflection increases, bellow-typepneumatic cylinders (as well as pneumatic artificial muscles) have afalling characteristic curve with significant non-linearity at a giveninternal pressure. The example from FIG. 2 or 3 is looked at below. Thecontact force acting on a surface to be contacted, in the steady state,is equal to the difference between the force F_(B) of the bellow-typepneumatic cylinder 34 and the restoring force F_(K) of the spring 36. Inthe case of an external contact force of zero, the adjusting path (thedeflection) of the handling apparatus is, however, limited to the rangeof the force-displacement characteristic curve which lies to the left ofthe point of intersection between the spring characteristic curve andthe actuator force characteristic curve. Where a contact force isgreater than zero, the maximum adjusting path is correspondinglysmaller. In order to be able to actually utilize the theoreticallypossible maximum lift of the linear actuator, it would be desirable forthe spring characteristic curve to also have a falling characteristiccurve (see adapted characteristic curve F_(K)′). In the ideal case, thespring characteristic curve would have the identical form as theactuator force characteristic curve. The offset—in this case adjustableby means of changes in pressure—between the characteristic curves thencorresponds to the contact force which would be generatableindependently of the deflection of the actuator if the characteristiccurves were adapted in this manner.

FIG. 8 shows a possibility of how, by means of a simple kinematicarrangement, the spring force characteristic curve is able to be adaptedto the characteristic curve of the actuator—at least approximately. Inthe case of the mechanism shown in FIG. 8, the bearings 361 and 362 arerigidly connected to a flange part (for example the interface 31 to themanipulator) and the top end of the connecting rod 363 is connected tothe other flange part (for example the holder 32 for the tool). A guidelever 364, which is for example L-shaped, is pivotably mounted on thebearing 362. The spring 36 (with an approximately linear characteristiccurve) is clamped between the end of a leg of the guide lever 364 andthe bearing 361. The connecting rod 363 is arranged between the end ofthe other leg of the guide lever 364 and the second flange part. Thespacing between the two flange parts 31 and 32 is shown by means of thereference h_(P) in FIG. 8. The force-displacement characteristic curveof the restoring force that acts between the plates in dependence on thespacing h_(P) is shown in FIG. 9 b. FIG. 9a shows the relationshipbetween the length of the spring and the spacing h_(P). As can be seenin FIG. 8 b, the force-displacement characteristic curve of the systemshown in FIG. 8, which is made up by the spring and the guide mechanism,is the same as the force-displacement characteristic curve of abellow-type pneumatic cylinder or of a pneumatic artificial muscle, as aresult of which the possible lift of a static friction-free pneumaticlinear actuator can be utilized in a considerably better manner.

As a result of the static friction-free design, a handling apparatusaccording to the embodiments described herein can also be operated asonly a “supple” (i.e. flexible) sensor unit for the contact force. Inthis case, the positioning of the tool is effected in part orexclusively by means of the manipulator (cf. manipulator 20 in FIG. 1).In this case, both a “mixed mode” and a “sensor-guided mode” areconceivable. In the “mixed mode”, small and high-frequency adapting ofpositions and regulating the force are carried out by the handlingapparatus, whereas the large-area, higher-ranking movement (roughpositioning) is ensured by the manipulator. In the “sensor-guided mode”,the handling apparatus acts as a passive sensor unit and the regulatingwork is carried out by the manipulator. The flexibility of such a sensorunit nevertheless allows the force to be regulated in a substantiallyjerk-free manner. In a pure sensor mode, the flexibility of theapparatus, that is the force-displacement performance characteristic(also called impedance) is also actively adjustable and adaptable to therespective application.

Information (measuring data) determined by means of the handlingapparatus concerning the contact force and/or the position of the toolin relation to the end effector flange of the manipulator is fed back tothe drive (or the drive units) of the manipulator in both cases (during“mixed mode” as well as “sensor-guided mode). In contrast to this, in“stand alone mode” the handling apparatus works independently of themanipulator and there is no feedback of measured data determined bymeans of the handling apparatus to the drive control means or driveregulating means of the manipulator. The manipulator executes apredetermined movement (for example to position the tool on theworkpiece). Precision control and regulating the force are assumed bythe handling apparatus, as described above, independently of themanipulator.

As a result of the inherent elasticity of the static friction-freelinear actuator and the restoring spring, the handling apparatus (bothin the mode as active flange and in pure measuring mode) protects themanipulator from jerks, impacts and similar short-term events whichresult in a sudden increase in the contact force and which a usual robotregulating means is not able to compensate.

In order to increase the accuracy of the force measurement, a load cellcan be arranged between a linear actuator and a flange part 31 or 32such that the force is not only determined in an arithmetical manner(for example from the direction of movement, the pressure and thedeflection) but can also be measured directly.

One exemplary embodiment relates to a method for handling objects or forprocessing surfaces with a manipulator, a handling apparatus which isarranged on the manipulator as shown, for example, in FIGS. 2 to 5 and atool which comes into contact with the object or the surface. The methodincludes positioning the tool by correspondingly deflecting the handlingapparatus such that contact force corresponds to a predetermined desiredvalue, it being possible for the desired value to be dependent on theposition of the manipulator. The method additionally includes handlingthe object (for example positioning, stacking, etc.) or machining thesurface (for example grinding, polishing, etc.). In this case, theposition of the tool and the contact force determined by means of thehandling apparatus are continuously monitored during handling ormachining operations and where desired are also logged. Consequently, aprocessing report can be prepared for every workpiece and the workpiececan be correspondingly classified (for example as B grade goods ifcertain force tolerances have not been adhered to during machining orhandling).

Some important aspects of a handling apparatus according to theembodiments described herein are summarized below:

A handling apparatus (active flange), which is suitable for automatedcontact tasks, includes as a mechanical interface, a first flange partfor releasably or fixedly connecting the handling apparatus to amanipulator, as well as a second flange part which is movable inrelation to the first flange part and is realized as a holder forreceiving a tool. At least one gearless, static friction-free actuatorserves to position the holder in relation to the first flange part. Inaddition, a sensor unit is provided to determine directly or indirectlythe force acting on the at least one actuator. Finally, a closed-loopcontrol unit ensures—on contact between a tool which is mounted on theholder and a surface—the regulating of the contact force in accordancewith a predeterminable time characteristic of the contact force (forceover time).

In addition, a mechanical guide device, which is mounted free ofstatic-friction (for example by means of a roller bearing or anair-cushion bearing), can be arranged between the two flange parts,whereby the mechanical guide device blocks all mechanical degrees offreedom except for those which are adjustable by the at least oneactuator. In the event of one single degree of freedom, for example arotationally fixed shaft guide can block all degrees of freedom up tothe one translatory degree of freedom which corresponds to the movementof the actuator.

The handling apparatus can additionally have a spring element whichgenerates a restoring force between the two flange parts and which isdirected in opposition to the effect of the force of the staticfriction-free actuator. The net force exerted onto an external body (forexample the workpiece) by the handling apparatus corresponds accordinglyto the difference between the actuator force and the restoring force ofthe spring.

Each gearless static friction-free actuator as well as theabovementioned spring element has a corresponding force-displacementcharacteristic curve. In the case of a simple spring, thischaracteristic curve is linearly ascending, in the case of a pneumaticactuator it is descending and pressure-dependent. Together thesecharacteristic curves determine the elastic performance characteristicof the handling apparatus (i.e. net force versus the position of theholder in relation to the manipulator). The closed-loop control devicecan be realized for the purpose of adjusting the force-displacementcharacteristic curve of the actuator (or of the actuators) such that thehandling apparatus has a predetermined elastic performancecharacteristic.

As already mentioned, the actuator may be a pistonless pneumaticactuator, a static friction-free pneumatic cylinder or an electricgearless direct drive. In the case of the electric direct drive, thereis a current-dependent force-displacement characteristic curve in placeof a pressure-dependent force-displacement characteristic curve.

In order to adapt the force-displacement characteristic curve of thespring element to the characteristic curve of the actuator in at leastan approximate manner, the outwardly effective force-displacementcharacteristic curve of the spring can be modified by a kinematicarrangement (i.e. a lever mechanism) to the force-displacementcharacteristic curve of the static friction-free pneumatic actuator.

The sensor unit can have a positional sensor for each actuator formeasuring the length (displacement) of the respective actuator. As analternative to this, it is possible to provide a sensor which isrealized for the purpose of determining the position of the holder inrelation to the first flange part (i.e. to the manipulator).

In the case of pneumatic actuators, the sensor unit can be realized forthe purpose of calculating the force acting on the actuator as well asthe position of the holder in relation to the first flange part from themeasured length (displacement) of the at least one and from the pressureprevailing in the actuator.

For applications under water or for applications where air flows are anuisance, an exhaust air duct of the pneumatic actuator may be connectedto a hose which directs the exhaust air away from the handling apparatusso that no air flows occur in the vicinity of the apparatus. Inaddition, the handling apparatus can be sealed against the incursion ofwater and/or dust.

A further example embodiment relates to a system including a manipulatorwith at least one degree of freedom, a handling apparatus fastened onthe manipulator as described above and a tool arranged on the handlingapparatus for contact tasks. In addition, a regulating unit forregulating the force exerted onto a workpiece by the tool is provided,wherein the regulating unit is realized for the purpose of roughlypositioning the workpiece by means of the manipulator and of carryingout the precise positioning and the regulating of the force by means ofthe handling apparatus.

As an alternative to this, the handling apparatus can be operated in apurely passive manner as a sensor unit and the force can be regulatedjust by means of the drive of the manipulator. In both cases there ismechanical decoupling between the workpiece and the inert mass of themanipulator by means of the adjustable elasticity of the handlingapparatus.

Although the invention has been illustrated and described with respectto one or more implementations, alterations and/or modifications may bemade to the illustrated examples without departing from the spirit andscope of the appended claims. In particular regard to the variousfunctions performed by the above described components or structures(units, assemblies, devices, circuits, systems, etc.), the terms(including a reference to a “means”) used to describe such componentsare intended to correspond—unless otherwise indicated—to any componentor structure, which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure, which performs thefunction in the herein illustrated exemplary implementations of theinvention.

In addition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“including”, “includes”, “having”, “has”, “with”, or variants thereofare used in either the detailed description and the claims, such termsare intended to be inclusive in a manner similar to the term“comprising”.

What is claimed is:
 1. An apparatus for automated contact tasks, theapparatus comprising: a mechanical interface for connecting the handlingapparatus to a manipulator; a holder for receiving a tool, the holderbeing movable in relation to the mechanical interface; at least oneactuator for positioning the holder in relation to the mechanicalinterface; a sensor unit configured to sense an actuator force providedby the at least one actuator; and a control unit that is configured to:set the actuator force to a desired minimum force to press the holderagainst a stop, while there is no contact between the tool and asurface; detect contact when the holder moves in relation to themechanical interface in opposition to the direction of the desiredminimum force; and regulate the actuator force according to apre-programmed contact force time-characteristic, when contact betweenthe tool and the surface has been detected, wherein, once contact hasbeen detected, the actuator force is increased from the minimum force toa desired contact force.
 2. The apparatus of claim 1, wherein thepre-programmed contact force time-characteristic defines an increase ofthe actuator force from the minimum force to the desired contact forcewithin a pre-programmable time interval.
 3. The apparatus of claim 2,wherein the actuator force increases linearly within thepre-programmable time interval.
 4. The apparatus of claim 1, wherein thecontrol unit is further configured to detect loss of contact.
 5. Theapparatus of claim 4, wherein the control unit is further configured toregulate the contact force, as a reaction to a detected loss of contact,such that the contact force is reduced to the minimum force.
 6. Theapparatus of claim 1, where the control unit is configured to detectloss of contact when the holder reaches the stop as a result of theactuator force.
 7. The apparatus of claim 6, wherein the sensor unitcomprises a displacement sensor configured to measure the relativeposition between the interface and the holder.
 8. The apparatus of claim1, wherein the control unit is configured to detect loss of contact whenthe speed of the holder in relation to the mechanical interface exceedsa predetermined threshold value.
 9. The apparatus of claim 8, whereinwhen loss of contact is detected, the speed of the holder in relation tothe mechanical interface is stored and contact is, again, detected whenthe speed of the holder in relation to the mechanical interface fallsbelow the stored speed.
 10. The apparatus of claim 1, further comprisinga spring element arranged between the mechanical interface and theholder to exert a restoring force on the actuator.
 11. The apparatus ofclaim 1, wherein: the actuator is a pneumatic linear actuator; thesensor unit comprises at least one position sensor associated with theat least one actuator and configured to measure the position of theholder in relation to the mechanical interface; and the sensor unit isconfigured to calculate the actuator force based on the measuredposition and a pressure prevailing in the pneumatic linear actuator. 12.The apparatus of claim 1, wherein the actuator is a pneumatic linearactuator, and wherein a duct forming an air outlet of the actuator isconnected to a hose which conducts the outlet air away from theactuator.
 13. A method for handling objects or for processing surfacesusing a manipulator carrying a handling apparatus that includes at leastone actuator coupling a mechanical interface, which is connected to themanipulator, with a holder, on which a tool is mounted, the methodcomprising: setting an actuator force to a desired minimum forcepressing the holder against a stop, while there is no contact betweenthe tool and a surface; detecting contact when the holder moves inrelation to the mechanical interface in opposition to the direction ofthe desired minimum force; and regulating the actuator force accordingto a pre-programmed contact force time-characteristic, when contactbetween the tool and the surface has been detected, wherein, oncecontact has been detected, the actuator force is increased from theminimum force to a desired contact force.
 14. The method of claim 13,wherein the pre-programmed contact force time-characteristic defines anincrease of the actuator force from the minimum force to the desiredcontact force within a pre-programmable time interval.
 15. The method ofclaim 14, wherein the actuator force increases linearly within thepre-programmable time interval.
 16. The method of claim 13, furthercomprising: detecting loss of contact between the tool and the surface;and reducing the actuator force to the desired minimum force when lossof contact has been detected.
 17. The method of claim 16, whereindetecting loss of contact comprises: detecting when the holder reachesthe stop as a result of the actuator force.
 18. The method of claim 17,wherein detecting when the holder reaches the stop comprises: measuringthe relative position of the holder in relation to the mechanicalinterface; and determining whether the holder has reached the stop basedon the measured relative position.
 19. The method of claim 16, whereindetecting loss of contact comprises: detecting when the speed of theholder in relation to the mechanical interface exceeds a predeterminedthreshold value.
 20. The method of claim 19, further comprising:detecting contact again, when the speed of the holder in relation to themechanical interface falls below the stored speed.